Widgit Symbols Schema
Temperature and Sound
Hot and Cold:
Heat uses wavy heat lines, but images for cold i.e. snowflake are not universal and therefore the alternative zig-zag lines will be used.
Speak uses the speech bubble. Content is added to the speech bubble where appropriate e.g. allow = say OK.
Sound, however uses the speaker element because words are not necessarily being used e.g. animals or objects which make a sound.